Copper trolley wire has been in commercial use for a long time. There is a standard set forth by the American Society for Testing and Materials (ASTM), as ASTM B47-95a, which is titled the Standard Specification for Copper Trolley Wire and which is reproduced in the Appendix to this specification. It is well known and straight forward for those of skill in this art to make copper trolley wire in accord with this ASTM standard.
This ASTM standard lists the minimum acceptable mechanical properties for copper trolley wire at various wire sizes. For example, grooved wire of a copper and silver alloy having a nominal area of 300,000 circular mils(cmils) is required by the ASTM standard to have a minimum tensile strength of 48,000 pounds per square inch (psi).
Table 1 below contains the tensile requirements for silver bearing round wire found in Table 1 of ASTM 47-95a, which is reproduced in the Appendix as Table 3. Table 2 below contains the tensile requirements for silver bearing grooved wire found in Table 2 of ASTM 47-95a, which is reproduced in the Appendix as Table 4.
TABLE 1 ASTM B47-95a Tensile Requirements For Silver-Bearing Round Wire Tensile Diameter, Area, Strength, min. in. cmils psi 0.5477 300000 48500 0.4600 211600 51500 0.4096 167800 53000 0.3648 133100 54000 0.3249 105600 55000
TABLE 1 ASTM B47-95a Tensile Requirements For Silver-Bearing Round Wire Tensile Diameter, Area, Strength, min. in. cmils psi 0.5477 300000 48500 0.4600 211600 51500 0.4096 167800 53000 0.3648 133100 54000 0.3249 105600 55000
Typical methods for manufacturing copper trolley wire that meets the ASTM standard include methods such as continuous casting, rolling, and/or drawing (e.g., area reduction) and combinations thereof. Such methods are disclosed, for example, in Avitzur, Handbook of Metal Forming Processes (John Wiley & Sons 1983). These known methods are sometimes referred to as cold working and in some instances utilize an annealing step. Another known method for producing copper trolley wire meeting the minimum ASTM standards is to begin with a large wire bar, and drawing and/or rolling the wire bar to the desired dimension.
However, copper trolley wire manufactured in the typical way is limiting to the design of rail systems using such wire. For example, in a rail system using copper trolley wire, substations for electrical power must be placed at certain distances apart from each other. If it is desired to reduce the number of substations, copper trolley wire made to comply with the ASTM standard is inadequate because it lacks the desired tensile strength. Also for example, the advent of high speed rail and the desire to reduce costs have exposed practical limitations in copper trolley wire that has the mechanical properties listed in the ASTM standard.
Therefore, it has become desirable to have a copper trolley wire that has improved mechanical properties. It is also desirable to obtain such improved mechanical properties in copper trolley wire using a commercially acceptable manufacturing process, namely a process that is not cost prohibitive. Specifically, the need is to develop a trolley wire that can provide rail design options not currently available and that can withstand the rigors of high speed rail transit, while still providing sufficient transfer of electricity.
Therefore, it is an object of this invention to provide a copper trolley wire with improved mechanical properties. More specifically, it is an object of this invention to provide a copper trolley wire with tensile strength well exceeding the minimum listed in the ASTM standard.
It is also an object of this invention to provide a method of making copper trolley wire with improved mechanical properties. Further, it is an object of this invention to provide a method of making copper trolley wire in a commercially feasible manner.